JP3079564B2 - Inverter power circuit - Google Patents

Description

The present invention relates to an inverter power supply circuit, and particularly to a DC-AC push-pull inverter power supply circuit.

[Conventional technology]

Conventionally, as a DC-AC push-pull inverter power supply circuit in a switching regulator, those shown in FIGS. 3 and 4 have been proposed. In FIG. 3, a DC power supply 1 obtained by voltage conversion by a DC-DC converter 2 is intermittently switched by switching elements 3 and 4, and a voltage is converted by a conversion transformer 5 to obtain an AC output. . In this case, the switching elements 3 and 4 are driven at a fixed duty. 4 includes a feedback diode 8 and a step-up / step-down inductor 9. By controlling the drive duty of the switching elements 3 and 4, the inverter power supply circuit itself has an output stabilizing function. ing.

Note that a rectifying / smoothing circuit 6 is connected to these DC-AC inverter circuits as shown by a virtual line, and is connected to a load circuit 7.

[Problems to be solved by the invention]

In such a conventional inverter power supply circuit, a rectangular wave is used as a signal for driving the switching elements 3 and 4, so that the driving signals of the switching elements 3 and 4 have a higher frequency with higher efficiency and smaller size. In this case, there is a problem that the loss in the conversion transformer increases due to generation of harmonics. Also,
When a rectifier is connected to the secondary side of the conversion transformer, there is a problem that noise is generated due to the reverse recovery characteristic of the rectifier.

In order to improve these, a resonance type inverter circuit in which a resonance circuit including a primary inductance of a conversion transformer and a coupling capacitor is inserted has been proposed. However, it is not easy to select a constant of the resonance circuit. When the characteristic is used, there is a problem that it is difficult to perform duty control and the circuit becomes complicated.

An object of the present invention is to solve these problems and provide a low-loss, low-noise inverter power supply circuit.

[Means for solving the problem]

The inverter power supply circuit according to the present invention, as a drive circuit for switching the switching element on and off, means for generating a first conversion frequency signal lower than the self-resonance frequency of the conversion transformer;
Means for generating a second converted frequency signal higher than the self-resonant frequency. The switching element is driven by a signal obtained by pulse width-modulating the first converted frequency signal with the second converted frequency signal. Constitute.

In this case, the first converted frequency signal is a reference sine wave signal, and the second converted frequency signal is a triangular wave signal.

[Action]

ADVANTAGE OF THE INVENTION According to this invention, a conversion element is driven by the signal which carried out pulse width modulation of the 1st conversion frequency signal lower than the self-resonance frequency of a conversion transformer with the 2nd conversion frequency signal higher than a self-resonance frequency, Only the first conversion frequency can be generated on the secondary side of the transformer.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. In the figure, 1 is a DC power supply, 3 and 4 are switching elements, 5
Is a conversion transformer, which intermittently connects the DC power supply 1 with the switching elements 3 and 4 on the primary side of the conversion transformer 5 to generate a voltage on the secondary side.

As a control circuit for the switching elements 3 and 4, a reference sine wave generating circuit 10 for generating a first converted frequency signal and a triangular wave synchronizing signal generating circuit for generating a second converted frequency signal
11 and a half-wave dividing circuit for dividing the reference sine wave for each half-wave
12, a pulse width modulation circuit 13 that includes PWM comparators 14 and 15 and performs PWM modulation of the divided half-sine wave with a triangular wave,
An output voltage detection circuit 16 for controlling the amplitude of the reference sine wave.

Here, the first conversion frequency signal is set to be lower than the self-resonant frequency of the conversion transformer 5, and the second conversion frequency signal is set to be higher than the self-resonance frequency of the conversion transformer 5.

According to this configuration, the first converted frequency signal from the reference sine wave generating circuit 10 is divided into two half-waves whose phases are shifted by 180 ° by the half-wave dividing circuit 12, as shown in part of the waveform in FIG. The wave signal 17 is divided. The two half-wave signals 17 are output from the PWM comparators 14 and 15 in the pulse width modulation circuit 13, respectively.
The signal is compared with a triangular wave synchronizing signal 18 as a second converted frequency signal from the triangular wave synchronizing signal generation circuit 11, and becomes a pulse width modulated switching drive signal 19.

The switching elements 3 and 4 have a phase of 180
It is driven by a sine-wave approximated switching drive signal 19 generated from the two half-wave signals shifted from each other. When the switching elements 3 and 4 are driven to interrupt the DC power supply 1, an AC signal of a required voltage is output to the secondary side of the conversion transformer 5. At this time, since the first conversion frequency is set lower than the self-resonant frequency of the conversion transformer 5 and the second conversion frequency is set higher than the self-resonance frequency of the conversion transformer 5, the second conversion frequency of the conversion transformer 5 is Not transmitted, only a sine wave at the first conversion frequency is generated at the output.

Moreover, since the amplitude of the sine wave is controlled in the reference sine wave generation circuit 10 by the signal from the output voltage detection circuit 16, the amplitude of the output voltage can be controlled, and the output voltage can be easily stabilized only by the inverter circuit. It can be aimed at.

Note that the output voltage detection circuit 16 may control the level of the direct current component at the base of the half-wave signal 17 generated in the half-wave division circuit 12 to stabilize the output voltage.

〔The invention's effect〕

As described above, according to the present invention, a switching element is driven by a signal obtained by pulse width-modulating a first converted frequency signal lower than the self-resonant frequency of a conversion transformer with a second converted frequency signal higher than the self-resonant frequency. Therefore, only the first conversion frequency can be generated on the secondary side of the conversion transformer. As a result, generation of harmonic components can be suppressed, and loss in the conversion transformer can be reduced. Further, noise when a rectifier is connected to the secondary side can be reduced. The output voltage can also be stabilized by controlling the amplitude of the reference sine wave or controlling the DC level of the half-wave signal.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of one embodiment of the present invention, FIG. 2 is a waveform diagram of a main part in the configuration of FIG. 1, and FIGS. 3 and 4 are block circuit diagrams of different conventional inverter power supply circuits. It is. 1 DC power supply, 2 DC-DC converter, 3, 4 switching element, 5 conversion transformer, 6 rectifier / smoothing circuit, 7 load circuit, 8 feedback diode, 9
…… Inductor for buck-boost, 10 …… Reference sine wave generation circuit,
11: Triangular wave synchronization signal generation circuit, 12: Half-wave division circuit,
13 …… Pulse width modulation circuit, 14,15 …… PWM comparator,
16 output voltage detection circuit, 17 half-wave signal, 18 triangular wave synchronization signal, 19 switching drive signal.

Claims (2)

(57) [Claims] In an inverter power supply circuit in which a DC power supply on a primary side of a conversion transformer is intermittently connected by a switching element to obtain an AC voltage on a secondary side, a driving circuit for intermittently switching the switching element is provided. Means for generating a first converted frequency signal lower than the self-resonant frequency, and means for generating a second converted frequency signal higher than the self-resonant frequency; An inverter power supply circuit, wherein the switching element is driven by a signal pulse width modulated by a signal. 2. The inverter power supply circuit according to claim 1, wherein the first converted frequency signal is a reference sine wave signal, and the second converted frequency signal is a triangular wave signal.